These studies will use cells immortalized by the fusion of embryonic day 18 murine corpus striatum with a murine neuroblastoma (N18TG2) to characterize the regulation of dopamine receptor/effector systems in a model system of central nervous system origin. These studies will use radioligand binding assays to quantify the density, ligand affinity and pharmacological properties of the ligand binding sites. Receptor linked second-messenger assays will be used to examine the interactions between binding sites and their coupling to second messenger systems. Differential expression of mRNA for the various components of these dopamine receptor/effector systems will be examined using molecular biological techniques. The cells will then be treated with combinations of non-specific (n-butyric acid, FGF) and specific differentiating agents (D1 agonists) to examine the effects of alterations in the neurochemical milieu on the phenotypic expression of dopamine receptors and their intramembrane stoichiometry. Dopaminergic systems and their receptors play a critical role in a number of psychiatric disorders. Dopamine receptor antagonism appears to be a key mechanism of action for neuroleptic agents. Understanding the complexity of the developmental determinants of dopamine receptor/effector expression could provide important information for understanding the pathology of these disorders as well as suggesting novel therapeutic interventions. The use of a cell line of neuronal origin avoids the conceptual and methodological problems associated with the intact CNS and provides a developmental expression system in which the determinants of dopamine receptor expression can be readily examined.